Continuous ceramic conveyor belts for use in processing items which are subjected to extremely high temperatures are known in the art. The ceramic belts convey the articles through a high temperature environment, or through other environments which would prove chemically destructive to metal or fabric belts. Prior ceramic belts have been manufactured either entirely of ceramic material, or only partially of ceramic material. Belts manufactured partially of ceramic materials can operate only within a limited temperature range, whereas belts manufactured entirely of ceramic materials have been limited by machining difficulties.
U.S. Pat. No. 2,986,387 to Illing discloses a ceramic belt for use in carrying tile or other types of ceramic ware through a tunnel kiln which is fired at a high temperature. The ceramic belt is formed partially of ceramic material and includes individual ceramic links interconnected by refractory metal cross rods. The ceramic links are elongated and have rounded ends with apertures extending transversely through the links at opposite rounded ends. The links are disposed in cross rows in a staggered relationship such that the forward end of one link is disposed between the adjacent and rearward ends of two links disposed in the preceding row. Similarly, the rearward end of the first link is disposed between adjacent forward ends of two other links disposed in the preceding row. The apertures of the links are aligned to create a plurality of parallel cross-passages extending through the belt. Thus, the ceramic belt includes a plurality of columns or strips, each strip including a plurality of spaced links.
The refractory metal cross rods are disposed through the cross-passages, and have ends extending beyond the sides of the outermost links of the belt. A bore extends transversely through the rods at the extending ends. End caps are disposed on the extending ends of the rods, and include openings which are aligned with the corresponding bores in the rod. A refractory metal retaining pin is inserted in the opening and extends through the bore. An air-setting refractory cement is plugged into the opening over the end of the pin to prevent the pin from escaping from the bore after the cement matures. Insertion of the pins thereby holds the cap on the extending end to hold the ceramic belt together.
However, since the belt of Illing is made only partially of ceramic material, the temperature range in which the belt can be used is limited by the usable temperature range of the non-ceramic, refractory metal. For example, the operative temperature range of the refractory metal is disclosed in the Illing patent as 1600.degree.-2400.degree. F. However, current high temperature processing can occur up to 4000.degree. F. Thus, in the disclosed structure of Illing the metal pin would be likely to melt at the desired extreme temperatures. Furthermore, in order for the refractory cement to perform the function of preventing escape of the pin, it would have to be bonded in the hole or else the cement plug would simply fall out. In practice, it is difficult to bond cement material to ceramic material and operate at the temperature range of 4000.degree. F.
Belts made totally of ceramic material overcome the temperature limitations of partial ceramic belts. However, ceramic materials which are suitable for use at these elevated temperatures are extremely hard in the fired or usable state. Machining the components after firing to provide a conventional means of holding the belt assembly together is either impossible, or at best, extremely difficult and economically unfeasible. For example, due to the small size of the cross rods and their circular cross sections, it is extremely difficult to drill holes in the cross rods if a cotter pin mechanism is to be used.
Due to the difficulty of machining fired ceramic components, previous attempts to make ceramic conveyor belts have involved either machining an edge fixation into the components in their "green" or unfired state when the components are extremely fragile, or making a belt without a mechanism for holding the edges of the belt together. The width of a ceramic belt with components machined in the "green" state has been limited by the fragility of the "green" components which had to be of a relatively small size in order to be handled and machined without excessive breakage. Using "green" components also has resulted in large quantities of scrap and has prevented stocking of belt components or repair parts until after an order had been placed identifying the specific size of belt required. A drawback of running a belt with unconnected components is that the components have a tendency to spread apart due to unwanted movement perpendicular to the direction of the belt drive, or disengage entirely from the belt.
In addition to the above problems in forming end fixations on ceramic belts, reliability problems have occurred in prior ceramic belt end fixation techniques. For example, when a conventional mechanical interlock such as a cotter pin or a threaded nut was used, the pins and nuts frequently became loose after a period of time. When glued or bonded components have been used, the reliability of the bond has been very limited in the high temperature range within which ceramic conveyor belts operate.